Remove uses of Path class from tests/standalone.

tests/standalone/io/secure_client_raw_server_test.dart

 // Copyright (c) 2013, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 //
 // VMOptions=
 // VMOptions=--short_socket_read
 // VMOptions=--short_socket_write
 // VMOptions=--short_socket_read --short_socket_write
 
 import "package:expect/expect.dart";
+import "package:path/path.dart";
 import "dart:async";
 import "dart:io";
 import "dart:isolate";
 
 const HOST_NAME = "localhost";
 const CERTIFICATE = "localhost_cert";
 Future<RawSecureServerSocket> startEchoServer() {
   return RawSecureServerSocket.bind(HOST_NAME,
                                     0,
                                     CERTIFICATE).then((server) {
@@ skipping 49 matching lines @@
       onDone: () {
         String reply = chunks.join();
         Expect.equals("Hello server.", reply);
         success.complete(server);
       });
   });
   return success.future;
 }
 
 void main() {
-  Path scriptDir = new Path(Platform.script).directoryPath;
-  Path certificateDatabase = scriptDir.append('pkcert');
-  SecureSocket.initialize(database: certificateDatabase.toNativePath(),
+  String certificateDatabase = join(dirname(Platform.script), 'pkcert');
+  SecureSocket.initialize(database: certificateDatabase,
                           password: 'dartdart');
 
   startEchoServer()
       .then(testClient)
       .then((server) {
         server.close();
       });
 }